Currently, nearly half of the online capacity of desalinated water is achieved through a reverse osmosis filtering process. Reverse osmosis market share is growing but current reverse osmosis technology remains capital and energy intensive, with limitations in product design and performance based upon current polymer filtration membranes. The current industry standard for polymer filtration is an eight inch diameter by forty inch length spiral wound membrane with 400 to 440 square feet of active membrane area. Such devices are limited in permeability which in turn limits output water per unit area, or flux, and requires increased membrane area and operating pressures. These high membrane area requirements and operating pressures are a result of membrane resistance (that is, permeability) as well as concentration polarization, scaling, fouling, and the like. As such, these filtration devices require frequent cleaning and ultimately replacement. The limitations in relation to the flux and associated membrane area requirements result in significant capital cost. The need for high operating pressure devices increase the energy required to operate the filtration device and which further results in degradation of the membrane due to fouling and compaction which also adds to the operating cost.
Current filtration devices for reverse osmosis utilize an eight inch diameter by forty inch length spiral wound design. Within the filtration media there are twenty to thirty-four membrane leafs which provide for an active membrane area for maximum filtration output. Although improvements have been made in the filtration media, these are only incremental improvements and do not address the issues raised in regard to limited flux throughput or the requirement for high operating pressures.
The reverse osmosis approach to filtering and/or desalination is to employ active filtering layers utilizing polyimide components. Such technology utilizes solution diffusion so as to separate the feed material into a concentrate and permeate. In the reverse osmosis technology, the membranes are susceptible to fouling, scaling and compaction. These materials also have limited chemical and biological resistance with limited methods of cleaning, which in turn relates to the need for frequent replacement of the filtration devices.
To protect the membrane materials, robust chemical conditioning and pretreatment is needed as a front end stage prior to desalination. Pretreatment is capital intensive and requires plant space, equipment, energy, and chemicals. Current pretreatment methods include conventional filtration and membrane filtration. Conventional filtration types include cartridge filtration and media filtration such as flocculation, sedimentation, dissolved air flotation, diatomaceous earth, granular media, pressure filters and gravity filters. Membrane filtration includes submerged microfiltration/ultrafiltration and pressurized microfiltration/ultrafiltration.
Furthermore, current state reverse osmosis membranes in some installations require multiple post treatment stages to achieve the desired product water. These additional stages require additional plant space and energy consumption.
Therefore, there is a need in the art for filtration devices that provide for improved flow characteristics, reduced size and weight and increased operational life while reducing or consolidating the demand for extensive pre-treatment and post treatment.